Fuel cell system

The degree of dryness in a fuel cell can be judged more accurately. A system has: an impedance calculation part that calculates an impedance of a fuel cell, extracts from the calculated impedance a high-frequency impedance which is an impedance in a high frequency range and a low-frequency impedance which is an impedance in a low frequency range, and subtracts the high-frequency impedance from the low-frequency impedance to calculate a differential impedance; a water content calculation part that calculates the water content of an electrolyte membrane using the high-frequency impedance and calculates the water content of a catalyst layer using the differential impedance; and a water content control part that performs water content recovery processing to increase the water content of the catalyst layer if the water content of the catalyst layer is smaller than a predetermined water content.